Manufacturers of engines meet set emissions regulations via aftertreatment systems. Tier 3, Interim Tier 4, and Final Tier 4 emissions regulations, for example, required substantial reductions in particulate matter (“PM”) and nitrogen oxides (“NOx”). Beyond the Final Tier 4 emissions regulation, drivers for the continued evolution of aftertreatment systems may include more stringent emissions standards; lower ownership costs, such as the initial cost of purchase; and more compact, modular solutions. Some aftertreatment systems include a diesel oxidation catalyst (“DOC”), a diesel particulate filter (“DPF”) for reducing PM, and a selective catalytic reduction (“SCR”) catalyst for removing NOx. Such systems may have relatively high ownership costs and require relatively large design spaces.
One way to reduce the design space of such a system is to decrease the volume between the DPF and the SCR catalyst, referred to as a mixing volume. Decreasing the mixing volume, however, presents challenges in getting adequate mixing of the exhaust gas and the reductant, so as to fully leverage the SCR catalyst's ability to reduce NOx levels.